.calculator-app-container {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
max-width: 800px;
margin: 0 auto;
background-color: #f9fafb;
border: 1px solid #e5e7eb;
border-radius: 8px;
padding: 20px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calc-header {
text-align: center;
margin-bottom: 30px;
}
.calc-header h2 {
margin: 0;
color: #1f2937;
font-size: 28px;
}
.calc-grid {
display: grid;
grid-template-columns: 1fr 1fr;
gap: 20px;
}
@media (max-width: 600px) {
.calc-grid {
grid-template-columns: 1fr;
}
}
.input-group {
margin-bottom: 15px;
}
.input-group label {
display: block;
margin-bottom: 5px;
font-weight: 600;
color: #374151;
font-size: 14px;
}
.input-group input, .input-group select {
width: 100%;
padding: 10px;
border: 1px solid #d1d5db;
border-radius: 6px;
font-size: 16px;
box-sizing: border-box;
transition: border-color 0.2s;
}
.input-group input:focus, .input-group select:focus {
outline: none;
border-color: #2563eb;
box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}
.btn-calculate {
grid-column: 1 / -1;
background-color: #2563eb;
color: white;
border: none;
padding: 15px;
font-size: 18px;
font-weight: bold;
border-radius: 6px;
cursor: pointer;
transition: background-color 0.2s;
margin-top: 10px;
width: 100%;
}
.btn-calculate:hover {
background-color: #1d4ed8;
}
.results-section {
grid-column: 1 / -1;
background-color: #ffffff;
border: 1px solid #e5e7eb;
border-radius: 8px;
padding: 20px;
margin-top: 20px;
display: none;
}
.results-section.visible {
display: block;
}
.result-row {
display: flex;
justify-content: space-between;
margin-bottom: 10px;
padding-bottom: 10px;
border-bottom: 1px solid #f3f4f6;
}
.result-row:last-child {
border-bottom: none;
margin-bottom: 0;
padding-bottom: 0;
}
.result-label {
color: #6b7280;
font-weight: 500;
}
.result-value {
font-weight: 700;
color: #111827;
font-size: 18px;
}
.big-total {
color: #059669;
font-size: 24px;
}
.seo-content {
margin-top: 50px;
padding-top: 30px;
border-top: 2px solid #e5e7eb;
color: #374151;
line-height: 1.6;
}
.seo-content h2 {
color: #1f2937;
margin-top: 30px;
}
.seo-content p {
margin-bottom: 15px;
}
.seo-content ul {
margin-bottom: 15px;
padding-left: 20px;
}
.seo-content li {
margin-bottom: 8px;
}
.error-msg {
color: #dc2626;
font-size: 14px;
margin-top: 5px;
display: none;
}
function calculateCompoundInterest() {
// Get inputs
var principalInput = document.getElementById('initialPrincipal').value;
var contributionInput = document.getElementById('monthlyContribution').value;
var rateInput = document.getElementById('interestRate').value;
var yearsInput = document.getElementById('yearsToGrow').value;
var frequencyInput = document.getElementById('compoundFrequency').value;
var errorBox = document.getElementById('errorBox');
var resultsDiv = document.getElementById('results');
// Reset UI
errorBox.style.display = "none";
errorBox.innerText = "";
resultsDiv.classList.remove('visible');
// Validate Inputs
if (principalInput === "" || rateInput === "" || yearsInput === "") {
errorBox.innerText = "Please fill in all required fields (Principal, Rate, and Years).";
errorBox.style.display = "block";
return;
}
var P = parseFloat(principalInput); // Principal
var PMT = contributionInput === "" ? 0 : parseFloat(contributionInput); // Monthly Contribution
var r = parseFloat(rateInput) / 100; // Annual Rate as decimal
var t = parseFloat(yearsInput); // Years
var n = parseFloat(frequencyInput); // Compounds per year
// Validate Numbers
if (isNaN(P) || isNaN(PMT) || isNaN(r) || isNaN(t) || P < 0 || t <= 0) {
errorBox.innerText = "Please enter valid positive numbers.";
errorBox.style.display = "block";
return;
}
// Calculation Logic
// 1. Future Value of the Initial Principal
// Formula: A = P * (1 + r/n)^(n*t)
var futureValuePrincipal = P * Math.pow((1 + (r / n)), (n * t));
// 2. Future Value of the Series of Contributions
// This is slightly complex because contributions are usually monthly, but compounding might be different.
// For this specific calculator, to keep accuracy high for standard users, we will treat contributions as being made at the end of every compounding period
// OR if frequency is 12 (monthly), it aligns perfectly.
// If frequency is different from contribution frequency, complex conversion is needed.
// To simplify for this specific web tool: We will assume contributions happen at the same frequency as compounding if n=12.
// If n != 12, we will approximate by annualizing the contribution or strictly adhering to the period.
// Refined Logic for Standard "Monthly Contribution" input:
// We need to iterate or use a specific formula.
// Let's use a loop for absolute precision regarding the monthly contribution interaction with specific compounding frequencies.
var totalBalance = P;
var totalContributed = P;
var months = t * 12;
for (var i = 1; i <= months; i++) {
// Add Interest
// Rate per month approximation for the loop:
// Effectively (1 + r/n)^(n/12) – 1 is the effective monthly rate
var effectiveMonthlyRate = Math.pow(1 + (r/n), n/12) – 1;
totalBalance += totalBalance * effectiveMonthlyRate;
// Add Contribution
totalBalance += PMT;
totalContributed += PMT;
}
// Results
var futureValue = totalBalance;
var totalInterest = futureValue – totalContributed;
// Formatting currency
var formatter = new Intl.NumberFormat('en-US', {
style: 'currency',
currency: 'USD',
});
// Display Results
document.getElementById('displayTotalValue').innerText = formatter.format(futureValue);
document.getElementById('displayPrincipal').innerText = formatter.format(totalContributed);
document.getElementById('displayInterest').innerText = formatter.format(totalInterest);
resultsDiv.classList.add('visible');
}
Compound Interest Calculator
Calculate how your investments grow over time with the power of compounding.
Monthly
Annually
Quarterly
Daily
Future Value:
$0.00
Total Principal Invested:
$0.00
Total Interest Earned:
$0.00
Understanding Compound Interest
Compound interest is often referred to as the "eighth wonder of the world." Unlike simple interest, where you only earn money on your principal investment, compound interest allows you to earn interest on the interest you've already accumulated. This snowball effect can significantly increase the value of your savings or investments over long periods.
How This Calculator Works
This calculator uses the standard compound interest formula extended to include regular monthly contributions. It calculates the future value of your investment based on four key inputs:
- Initial Investment: The amount of money you start with.
- Monthly Contribution: Money added to the investment on a regular basis.
- Interest Rate: The expected annual rate of return (e.g., 7% for stock market average).
- Compounding Frequency: How often the interest is calculated and added back to the principal.
The Math Behind the Calculation
The calculation is performed in two parts. First, we calculate the future value of the initial lump sum. Second, we calculate the future value of the series of monthly contributions. The formula used for the lump sum is:
A = P(1 + r/n)^(nt)
Where:
- P = Initial Principal
- r = Annual interest rate (decimal)
- n = Number of compounding periods per year
- t = Time in years
Why Start Early?
Time is the most significant factor in compound interest. Because the exponent in the formula involves time (years), holding an investment for 30 years versus 20 years yields exponentially higher returns, not just linear ones. Using this tool, you can visualize how small increases in your monthly contribution or interest rate can dramatically change your financial future.